1. Field of the Invention
The present invention relates to a substrate processing apparatus and a focus ring, and in particular to a substrate processing apparatus that can improve the efficiency of heat transfer between a mounting stage and a focus ring.
2. Description of the Related Art
In the case of carrying out plasma processing such as etching processing on a wafer as a substrate, the width and depth of trenches formed on a surface of the wafer through etching are affected by the temperature of the wafer, and hence the temperature of the entire surface of the wafer is required to be maintained uniform during the etching processing.
A substrate processing apparatus that subjects a wafer to the etching processing has a chamber that houses the wafer and can be evacuated, and a mounting stage (hereinafter referred to as the “susceptor”) on which the wafer is mounted during the etching processing. In the evacuated chamber, plasma is generated, and the wafer is etched by the plasma. The susceptor has a temperature controlling mechanism to control the temperature of the wafer. When the wafer is subjected to the etching processing, the temperature of the wafer rises because it is exposed to heat from the plasma, and thus the temperature controlling mechanism of the susceptor cools the wafer so as to maintain the temperature of the wafer constant.
Moreover, an annular focus ring made of, for example, silicon is mounted on the susceptor such as to surround a peripheral portion of the wafer. The focus ring focuses the plasma in the chamber onto the wafer. The focus ring is also exposed to heat from the plasma during the etching processing, and as a result, the temperature of the focus ring rises to, for example, about 300° C. to 400° C.
During the etching processing, most of the wafer is cooled by the temperature controlling mechanism of the susceptor, but the peripheral portion of the wafer is affected by heat radiated from the focus ring, and it is thus difficult to maintain the temperature of the entire surface of the wafer uniform.
Conventionally, because the focus ring is merely mounted on the susceptor, the focus ring and the susceptor do not adhere to each other, and hence the efficiency of heat transfer between the focus ring and the susceptor is low. As a result, heat accumulates in the focus ring, and the temperature of the focus ring cannot be maintained constant, and it is thus difficult to carry out the etching processing uniformly on a plurality of wafers in the same lot.
In view of the foregoing, it is necessary to actively control the temperature of the focus ring. Accordingly, a method of improving the efficiency of heat transfer between the focus ring and the susceptor and actively controlling the temperature of the focus ring using the temperature controlling mechanism of the susceptor has been developed (see, for example, Japanese Laid-Open Patent Publication (Kokai) No. 2002-16126). In this method, a heat transfer sheet is provided between the focus ring and the susceptor so as to improve the efficiency of heat transfer between the focus ring and the susceptor.
However, if the heat transfer sheet is provided between the focus ring and the susceptor, an interface arises between the focus ring and the heat transfer sheet, and also, an interface arises between the heat transfer sheet and the susceptor. The degree of adhesion at each interface is improved as compared with the case where the focus ring and the susceptor are in direct contact with each other, but some minute gaps still remain at each interface. Because the focus ring, heat transfer sheet, and susceptor are placed in an evacuated environment, the minute gaps form a vacuum insulation layer, and each interface obstructs heat transfer. Thus, there is a problem that the efficiency of heat transfer between the focus ring and the susceptor has not been satisfactorily improved.